1 Ghost: So how are we supposed to stop this wizard from blowing up the mountains?2 Mordekai: Drain all the mana he's gathering.3 Mordekai: Don't ghosts have an energy drain attack or something?4 Ghost: If we did, I wouldn't be talking to you...

In early version of Dungeons & Dragons, ghosts had a special attack known as an
energy drain, which is jargon for
an effect which removes levels of experience from a character, making them weaker in all of their various skills. In more recent version this
has shifted to a more specific ability drain, which merely makes them weaker in such things as strength or intelligence.

I'm not really sure where this characterisation of ghosts came from. As far as I'm aware, nobody who has (allegedly) encountered a ghost
has come out of it with reduced skills and abilities.